How to mutate a list with a function in python?

Question

Here\'s a pseudocode I\'ve written describing my problem:-

func(s):
   #returns a value of s

x = a list of strings
print func(x)
print x #these two should          


        

Answer 1

func(s):
   s[:] = whatever after mutating
   return s

x = a list of strings
print func(x)
print x

You don't actually need to return anything:

def func(s):
    s[:] = [1,2,3]

x = [1,2]
print func(x)
print x # -> [1,2,3]

It all depends on what you are actually doing, appending or any direct mutation of the list will be reflected outside the function as you are actually changing the original object/list passed in. If you were doing something that created a new object and you wanted the changes reflected in the list passed in setting s[:] =.. will change the original list.